In addition to the common solid type of electrical conductor consisting simply of a continuous rod-like body of solid metal in an apt diameter, electrical conductors typically are composed of groupings of a plurality of individual metal strands arranged or laid down in any one of a number of different cable patterns or schemes common to the art, for example, concentric lay, concentric parallel lay, concentric cross lay, annular, segmental, rope stranded, bunched, and the like.
Concentric lay stranded conductors are typically constructed with a single central or core strand having one layer of six strands, or a multiplicity of layers of strands with the number of strands in each succeeding overlying layer increasing in every layer in multiples of six strands, for example, six, twelve, eighteen, twenty-four, et seq., concentrically arranged about the axis of the conductor such as each of said layers of strands being sequentially helically wound concentrically around the single central or core strand. A concentric parallel lay strand pattern comprises an arrangement wherein the strands or layers of strands are helically wound in the same direction concentrically around the central or core strand, whereas a concentric cross lay strand pattern comprises an arrangement wherein each succeeding overlying layer of strands is helically wound in an alternatingly opposite direction to any adjoining layer of strands, either below or above.
Moreover, certain of these types of stranded cable electrical conductors can be consolidated to various degrees, such as the compressed or compacted conductors of various strand pattern shown in U.S. Pat. Nos. 1,943,087; 3,164,670; 3,234,722; 3,352,098; 3,383,704; 3,444,684; 3,760,093; and 3,823,542. Compressed stranded conductors are generally defined as "one or more layers of any stranded conductor consisting of seven wires or more" which have been compressed to reduce the outside diameter of the conductor by not more than three percent. Note, for instance ASTM-B8-72. Compacted stranded conductors generally comprise those stranded conductors which have been compacted to an outside diameter of more than 3 percent, such as, for example, compacted up to about eight to ten percent. The application of pressure for the consolidation of stranded cable conductors in forming either compressed or compacted types of products can be applied either in a single pressing to the exterior of the completed composite assembly of strands making up the conductor, or in a series of pressings in sequence to several or all layers of strands individually following their winding about the underlying unit, such as in U.S. Pat. Nos. 1,943,087; 3,383,704; and 3,760,093.
Although each of the prior types of stranded cable designs, such as referred to above, may be outstanding or superior in one or more particular properties or attributes, such as degree of flexibility, or on the other hand provide a saving in insulating covering material due to a compaction reduced diameter, each of said designs entails some offsetting shortcomings and thus none provides an overall improved and outstanding electrical cable of all-around enhanced properties or attributes.
For instance, the compressing of multi-layered, concentric lay cables having succeeding overlying layers of strands helically wound in opposite directions, to reduce their diameter, either by means of a single compressing force applied only to the exterior of the assembled composite of overlying layers of strands or in a series of substantially equal compressing forces applied in sequence to each layer of strands as formed, results in indentations or notches being impressed into the individual strands of the layers at the location of their crossing contacts or intersections with strands of adjoining layers. The presence of any surface irregularities in the strands, such as indentations or notches, evidently constitutes a substantial detriment both in the manufacturing operation for producing insulated conductors with such a cable, and in the performance of the product thereof. For example, indentations or notches impressed in the strands at their intersections with crossing strands of an adjoining layer reduces flexability by providing mortice-like connections or grips between the strands which resist relative movement of the strands or their layers when subjected to bending or flexing.
However, when such a cable construction is to be enclosed within an extrusion molded plastic covering such as is common in insulated electrical conductors, the presence of indentations or notches in the strands causes a far greater detriment than detracting from flexibility. Namely, the forced bending or flexing of such a compressed, concentric cross lay stranded cable, such as is inherent in manufacturing operations, in moving around capstans or winding on reels, and thereafter in service, wrenches the mortice-like gripped or locked strands loose, prying them from their restraining intersecting indentations or notches and driving them from their initial relative positions and arrangement, thereby distorting and stretching or extending the shape and length of such strained strands. This distortion and stretching of the force displaced strands frequently causes a disarrangement or separation of the parallel contacting arrangement of the layers of strands, particularly in the outermost layer of strands, and the radial expansion or bulging of the strands which results in significant open spaces or gaps therebetween. The presence of any such openings or gaps in the outermost layer of distorted and stretched strands permits the adverse entry and internal dispersal of plastic materials, such as semiconducting or insulating compositions, during extrusion molding of coverings or coatings thereof over the stranded cable in the production of insulated electrical conductors. Heretofore, this shortcoming has necessitated the use of an intermediate barrier in the form of a film or tape applied over the assembled stranded cable and thus intermediate the stranded cable and the plastic covering or enclosure extruded thereover.
The effects of prior art compressing means upon such cross lay stranded cable with the impression of indentations or notches, and the resultant disarrangement or separation due to distortion and stretching, is diagrammatically illustrated in FIGS. 4, 5 and 6.
For example, as shown in FIG. 4, indentations, identified as I, are impressed in the underlying layer of strands, identified as U, caused by compressing the overlying layer of strands, identified as O. In FIG. 5 the indentations I are shown in a strand of an underlying layer U resulting from compressing the overlying layer of strands prior to an assembly of alternately helically wound strands for a cable being significantly flexed or bent, such as by coiled around a capstan or reel. The distance from the center of the assembly of alternately helically wound strands to the annular axis of a given overlying layer of strands O, or radius, is represented in FIG. 5 by the line R. In FIG. 6, the assembly of alternately helically wound strands for a cable of FIG. 5 is illustrated after significant flexing or bending such as by coiling around a capstan or reel, whereupon the strands of the overlying layer O are forced from their original position within the assembly and dislodged from within the adjoining indentation impressed in the underlying strand U, and the strands located in the outside of the bend become separated or spaced from each other with gaps therebetween. The dislodgement of the strands in an overlying layer O from within the compression formed indentations I of an underlying strand U, thus increases the radius R or distance from the center of the assembly of alternately helically wound strands to the annular axis of a given overlying layer of strands O, stretches the strands and separates the strands located in the outside of a bend.